You're not overreacting. I've also used Poloniex for over three years. And had no major problems until the last month or so. In fact I've recommended them on many occasions. However it's got to the point where I've pulled my funds and will only trade there in small amount & as a last resort until they get these issues sorted.
One truism in crypto is 'no Exchange is too big to fail'. And they usually start faltering before they topple over. I hope it is not the case for Poloniex however I'm unwilling to take the risk. Seen it happen too many times.
Yes I think it is worrying for those of us who were around during the GOX collapse.